The present invention relates generally to the field of endodontics, and more particularly to a method of applying a filler material in an endodontically prepared root canal.
Root canal therapy is a well-known procedure wherein the crown of a diseased tooth is opened so as to permit the canal to be cleaned and then filled. More particularly, a series of very delicate, flexible, fingerheld instruments or files are used to extirpate or clean out and shape the root canal, and each file is manually rotated and reciprocated in the canal by the dentist. Files of increasingly larger diameter are used in sequence, to achieve the desired cleaning and shaping. When the canal is thus prepared, it is obturated or solidly filled with a filling material, which typically comprises a waxy, rubbery compound known as gutta percha.
In the traditional method of obturating a root canal, strand-like pieces of gutta percha, commonly referred to as "points", are inserted into the extirpated root canal. The points are then physically compacted by a compactor, which may be heated, and which is manipulated into contact with the points to soften and compact the material into the canal. This is a time consuming procedure, and it is difficult to insure that all portions of the canal are filled.
The Thermafil.TM. compactor as sold by Tulsa Dental Products, consists of a compactor according to U.S. Pat. No. 4,871,312, with a manually engagable handle at one end. The opposite or distal end of the compactor is coated with a layer of alpha phase gutta percha. As hereinafter further described, alpha phase gutta percha has a somewhat different crystalline structure as compared to the more conventional beta phase, and alpha phase requires less heat to become plasticized than does beta phase.
To fabricate the Thermafil.TM. compactor, conventional beta phase gutta percha is placed in a cavity in a mold, and the mold is heated under conditions of controlled heat and time to plasticize the gutta percha, which also serves to convert the gutta percha to alpha phase. The distal end of the compactor is inserted into the gutta percha in the cavity, and upon cooling, the gutta percha solidifies about the distal end. When ready for use, the dentist heats the gutta percha by means of a separate heat source, such as an open flame, until the gutta percha again plasticizes. The compactor is then inserted into the root canal and manipulated by hand to cause the gutta percha to fill the canal.
In the above procedure, it is difficult for the dentist to control the application of the external heat, and if the gutta percha becomes too hot, it will unduly shrink upon cooling and voids will be formed in the canal, causing leakage.
U.S. Pat. Nos. 4,894,011 and 4,758,156 to Johnson disclose an obturating procedure which includes a carrier having a manual handle and a shaft with a reduced diameter portion which is designed to fail when a certain level of torque is applied. Gutta percha is molded to the carrier, and in preparation for use, the gutta percha is heated by an external source to a temperature at which the surface becomes "glossy". The heated instrument is then inserted into the root canal, and the handle is rotated until torsional failure occurs. Thus the distal end portion of the shaft remains in the canal.
The procedure of the Johnson patents involves the same limitations noted above with regard to the difficulty of controlling the temperature to which the gutta percha is heated by the external source, and the resulting problems of shrinkage and voids in the canal.
U.S. Pat. No. 4,457,710 to Dr. John McSpadden discloses a procedure for obturating extirpated root canals wherein a gutta percha point is placed in the canal. A compactor having downwardly facing shoulders is then inserted in the canal and rotated at a speed of about 6,000 rpm or less, to thereby mechanically work the gutta percha and generate frictional heat which plasticizes the material. The compactor is then withdrawn longitudinally, with the shoulders of the compactor forcing the plasticized gutta percha downwardly and laterally.
A disadvantage of the procedure described in the cited McSpadden patent is the fact that the diameter of the compactor must closely approximate the diameter of the root canal, in order to insure that sufficient frictional heat is developed to plasticize the gutta percha, which has a relatively high melting point. More particularly, the gutta percha must be forced against the wall of the canal to cause enough friction to plasticize it, and a large diameter compactor is needed for this purpose. The use of a compactor of large diameter in turn causes problems, in that it does not have the ability to readily extend through the curves which are common in root canals. Also, they tend to extrude the gutta percha through the apex of the canal.
Dr. McSpadden has recently suggested a new procedure wherein gutta percha is placed in a tube which is supplied to the dentist. In use, the dentist heats the tube using an external heat source, and the compactor is then inserted into the tube to coat its distal end. The compactor with the heated gutta percha coating is then immediately inserted in the canal, together with an additional point of cold gutta percha, and the instrument is machine rotated at a relatively slow speed of about 2,000 rpm. The additional point of gutta percha is used to avoid an excessive amount of heated gutta percha with the attendant risk of shrinkage and voids. Also, the relatively slow speed is employed so as to avoid plasticizing the solid additional point, again to avoid the risk of overheating and shrinkage. This is seen to be a rather cumbersome procedure for the dentist, and there is a risk that the gutta percha in the tube may be overheated, causing its deterioration.
It is accordingly and object of the present invention to provide a method of applying gutta percha in an endodontically prepared root canal, and which avoids the above noted limitations and disadvantages of the prior art techniques.
It is a more particular object of the present invention to provide a method of the described type which utilizes only the frictional heat generated by the rotation of the compactor to plasticize the gutta percha, and which thereby avoids the need to apply external heat to the gutta percha immediately before the instrument is inserted into the canal.
It is a further object of the present invention to provide a method of the described type which permits the use of a compactor of relatively small diameter which serves to minimize the risk of damage by contact of the compactor with the walls of the canal.
It is still another object of the present invention to provide a novel endodontic compactor for use in carrying out the method of the present invention.